In a mechanical seal device, various materials are applied in accordance with the intended use, to opposite sliding surfaces of a stationary sealing ring and a rotating sealing ring arranged opposite to the stationary sealing ring.
In a usage where contamination is particularly unfavorable, silicon carbide (SiC) that is less likely to cause wear is applied as a material for the sealing rings. Likewise, the aforementioned sealing rings made of SiC are adopted to stationary and rotating sealing rings of a mechanical seal to be used in a semiconductor manufacturing factory, a nuclear power related facility, or the like where for example, ultrapure water or pure water is used for clearing or cooling. However, a phenomenon where silicon dioxide (SiO2) accumulates on sliding surfaces of both of the sealing rings to cause surface whitening of the sliding surfaces has been confirmed.
SiO2 becomes a source of contamination of a sealed fluid, and in addition, due to the accumulation of SiO2, a deterioration of sealing performance of the sliding surfaces or a defect such as an occurrence of chipping or surface roughness of the sliding surfaces has been confirmed. The mechanism of chipping or surface roughness has not been precisely solved; however, these have been proved from studies of the inventors to be associated with the accumulation of SiO2 on the sliding surfaces.
The accumulation of SiO2, regarded as a factor for abnormal wear of the sliding surfaces is considered to be attributed to a high specific resistance value (equal to or higher than 4 MΩ·cm) of ultrapure water, pure water, or the like. Patent Citation 1 proposes a technique in which a SiC film having a specific resistance value of equal to or lower than 1 Ω·cm is deposited by chemical vapor deposition on a sliding surface of one of stationary and rotating sealing rings or on sliding surfaces of both of the sealing rings in order to prevent SiO2 from accumulating on the sliding surfaces.